KR20090104774A - Activated carbon catalyst - Google Patents

Abstract

PURPOSE: An activated carbon catalyst is provided to reduce the amount of nitric oxide in ammonia by converting the nitric oxide into nitrogen or water with activation. CONSTITUTION: An activated carbon catalyst includes the nitrogen content of 0.4 weight% or more, the micropore volume of 0.47 cm^3/g or less, and the macropore volume of 0.72 cm^3/g or less. A carbonaceous substance is contacted to a nitrogenous compound. The carbonaceous substance is gasified by the steam vapor, the nitrogen or a carbon compound at a temperature of 750°C or more. The nitrogenous material is simultaneously supplied to a reaction.

Description

Activated carbon catalyst

The present invention relates to an activated carbon catalyst capable of maintaining activity even in the presence of a catalyst poison, thereby converting nitrogen oxides into nitrogen and water in the presence of ammonia. The invention also relates to a process for preparing the activated carbon catalyst according to the invention and to the use of the same for the reduction of nitrogen oxides.

Nitrogen oxides are one of the exhaust components produced during the combustion process, and their allowable emissions must be continuously reduced due to environmental impacts. Reduction of nitrogen oxides occurs mainly with the aid of a catalyst.

Nitrogen oxide reduction processes are already known. These processes are generally known by the term "SCR process" and SCR means "selective catalytic reduction". These processes have been used for years in power plants, furnaces, waste incinerators, gas turbines, industrial plants and motors. This process is described in detail in DE 3428232 A1. The characteristic of this SCR process is that chemical reactions generally occur selectively in mineral-doped carbon-free catalysts, ie nitrogen oxides NO and NO ₂ are preferably reduced, while Each unwanted secondary reaction (eg, sulfur dioxide oxidized to sulfur trioxide) is removed to a very large extent.

Mixed oxides comprising V ₂ O ₅ (eg in the form of V ₂ O ₅ / WO ₃ TiO ₂ ) can be used as SCR catalysts. Zeolites are also known as catalytic converters.

In practical applications, ammonia or compounds which separate ammonia during application such as urea or ammonia formate are used as reducing agents in solid or dissolved form. According to Scheme (1), 1 mole of ammonia is required to convert 1 mole of nitrogen monoxide:

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)

The conversion product is the corresponding water (H ₂ O) and nitrogen (N ₂ ). Chemically, this conversion relates to the inproportionation of nitrogen oxides and ammonia to nitrogen.

Catalysts for the SCR process known in the prior art have the problem of very quickly losing catalytic activity in the presence of catalyst poisons in crude gas (eg, arsenic, boron, etc.). They are also unable to convert nitrogen oxides to nitrogen and water in the presence of ammonia in an acceptable temperature range, such as 90 to 160 ° C.

Typical SCR processes using commercially known SCR catalysts are not suitable for this problem, since the so-called heavy metals already deactivate the catalyst after a duration. The conversion temperatures required for typical SCR catalysts are also from 300 to 350 ° C., for example in the case of expensive new low temperature SCR catalysts disclosed in the examples of EP 0593790 A, temperatures of 160 ° C. or higher are also required. Therefore, there is an energy penalty due to the heating (calefaction) of the gas required at a temperature of 160 ℃ or more.

The present invention provides a catalyst which is sufficiently active even in the presence of a catalyst poison, which can reduce nitrogen oxides in the presence of ammonia, and a method for producing the same.

Starting from the prior art, the present invention provides a catalyst that is sufficiently active in the presence of a catalyst poison, thereby reducing nitrogen oxides in the presence of ammonia. The conversion is preferably carried out at a temperature in the range below 180 ° C., more preferably in the range from 90 to 160 ° C.

According to the invention the problem is solved by activated carbon catalysts having a specific nitrogen content and having specific pore volumes for micropores of less than 1 nm and macropores of greater than 1 nm.

Activated carbon catalyst according to the present invention

(a) the nitrogen content in the carbon frame is at least 0.4% by weight;

(b) the pore volume of small pores less than 1 nm is 0.47 cm 3 / g or less;

(c) The pore volume of large pores greater than 1 nm is characterized by being 0.72 cm 3 / g or less.

A first embodiment of the invention is an activated carbon catalyst having a nitrogen content of 0.4 to 0.5% by weight in the carbon framework.

A second embodiment of the invention is an activated carbon catalyst having a nitrogen content of 0.8 to 1.6% by weight in the carbon framework.

A third embodiment of the present invention is an activated carbon catalyst having a pore volume of less than 1 nm of pore volume of 0.2 cm 3 / g or less.

A fourth embodiment of the present invention is an activated carbon catalyst having a pore volume of small pores of less than 1 nm between 0.2 and 0.4 cm 3 / g.

A fifth embodiment of the present invention is an activated carbon catalyst having a pore volume of large pores greater than 1 nm of 0.5 cm 3 / g or less.

A sixth embodiment of the present invention is an activated carbon catalyst having a pore volume of large pores greater than 1 nm between 0.4 and 0.6 cm 3 / g.

A seventh and particularly preferred embodiment of the present invention has a nitrogen content of 0.5% by weight or less in the carbon skeleton, a pore volume of small pores of less than 1 nm of 0.2 cm 3 / g or less, and pores of large pores of more than 1 nm. Activated carbon catalyst having a volume of 0.4 cm 3 / g or less.

An eighth, particularly preferred embodiment of the present invention has a nitrogen content of at least 0.4% by weight, preferably 0.8 to 1.5% by weight, and a pore volume of small pores of less than 1 nm in a carbon skeleton of 0.2 to 0.4 cm 3 / g And an activated carbon catalyst having a pore volume of large pores greater than 1 nm between 0.4 and 0.6 cm 3 / g.

Activated carbon catalysts which meet the above requirements according to the invention are preferably in the presence of a catalyst poison, in the presence of ammonia or a compound which separates ammonia in the application, such as hexamethylenetetramine, urea or ammonium formate, It has been found suitable for conversion to nitrogen and water at temperatures of up to 160 ° C., in particular from 90 to 160 ° C. If ammonia is used, it may be in the form of gaseous ammonia or ammonia gas liquid (ammonia water) with varying concentrations of ammonia.

The examples show that the nitrogen atoms are specifically incorporated in the grid frame of the activated carbon catalyst according to the present invention to specifically increase the catalytic activity on NOx in the presence of ammonia or a compound which separates ammonia during application. Shows. It is also shown that not only the nitrogen content, but also the pore volume (measured by benzene adsorption and mercury porosimetry) affect the catalytic activity of the activated carbon catalyst according to the invention.

By specifically modifying these two parameters, it is possible to produce activated carbon catalysts having a variety of high catalytic activities and at suitable production costs for specific applications.

Further examples show that, even in the presence of heavy metals such as arsenic or boron, the catalytic activity on NOx reduction is almost preserved. Only slowly loading the activated carbon catalyst according to the invention results in slow deactivation. This means that in the use of activated carbon catalysts according to the invention in gas cleaning comprising nitrogen oxides (NOx) and heavy metals, not only nitrogen oxides but also toxic heavy metals are removed from the crude gas.

The activated carbon catalyst according to the present invention can be used as a whole catalyst and also as a catalyst provided in a carrier. If the catalyst according to the invention is developed as a catalyst provided on a carrier, this is achieved by grinding the catalyst according to the invention and applying it on a carrier material.

The invention also relates to a process for the preparation of the activated carbon catalyst according to the invention.

In general, the preparation of an activated carbon catalyst according to the invention is achieved by contacting a carbonaceous material with a compound comprising nitrogen.

The carbonaceous material is selected from all known materials suitable for the production of activated carbon, for example coconut shells, coal, lignite coke, turf coke and polymers. .

Urea is primarily used as a nitrogenous material. Ammonia (in the form of gaseous or aqueous solutions of varying concentrations), hexamethylenetetramine, polyacrylnitrille or melamine can be used.

The catalyst according to the invention is preferably prepared using a multistage fluidised bed.

In a preferred embodiment, the aqueous urea solution is added to the multistage fluidized bed as a nitrogenous compound. The concentration of urea solution is 45%. 2 to 10 kg of urea are used for 100 kg of carbonaceous material. A urea amount of 5 to 6 kg is particularly preferred for 100 kg of carbonaceous material.

The carbonaceous material is partially at least 750 ° C., preferably 800-900 ° C., in a fluidized bed reactor, pit furnace, rotary furnace or multilevel furnace. It is desirable and economical to gasify at a temperature with a mixture of steam, nitrogen and carbon dioxide, and to supply the nitrogen-containing material into the reactor at the same time. Gasified carbon of steam, nitrogen and carbon dioxide can be obtained by burning combustible materials including natural gas, oils or other hydrocarbons. This partial gasification inserts nitrogen into the carbon backbone and achieves the desired small pore and large pore systems. Small pore and large pore volumes increase as the partial gasification of the carbon skeleton is increased, whereby the catalyst according to the invention can be obtained by changing the partial gasification duration. Small pores and large pores increase with increasing partial gasification, but also increase manufacturing costs.

The invention also relates to the use of at least one of the activated carbon catalysts according to the invention for the reduction of nitrogen oxides.

The conversion of nitrogen oxides is preferably in the presence of ammonia (in gaseous form or in an aqueous solution of various ammonia concentrations) or an ammonia separation compound, for example urea or ammonia formate, preferably at temperatures up to 180 ° C., in particular 90 to 160 It is carried out at ℃.

A particular embodiment of the use according to the invention is when the crude gas to be treated comprises a catalyst poison such as arsenic or boron.

The invention also relates to the use of the activated carbon catalyst according to the invention in a sulfacid process. In this process, sulfur dioxide reacts with water and oxygen on wet activated carbon. The technical application of this process has been carried out under the name "sulfasid process" (Sulfur No. 117, March / April 1975, 32-38).

Activated carbon catalysts can be used in these processes in any form. For example, it can be used in combination with pellets, granules, powders or carrier materials.

In connection with the use of the activated carbon catalyst according to the invention for the reduction of nitrogen oxides, the activated carbon catalyst according to the invention can be used in combination with conventional SCR catalysts. The SCR catalyst can be used before or after the use of the carbon catalyst according to the invention. Of course, two or more catalysts according to the present invention may be used in a catalyst alignment.

The present invention will be described in more detail with reference to the following examples, which are not intended to limit the invention.

The activated carbon catalyst of the present invention can maintain activity even in the presence of a catalyst poison to convert nitrogen oxides to nitrogen and water in the presence of ammonia.

Preparation of Activated Carbon Catalysts

To improve the basic idea, samples with different nitrogen content and different small and large pore volumes were prepared. The 8 mm fluidized bed reactor was fed 600 kg of coal briquettes of 4 mm shape per hour. The furnace temperature was about 900 ° C., burning natural gas to produce a flowing gas. 300 g of steam per hour was fed to partially gasify the 4 mm shaped bracket product. Samples 1 and 2 (comparative example) were prepared without adding a nitrogen compound. Another activated carbon catalyst sample was prepared by feeding urea (in the form of 45% aqueous solution), a nitrogenous compound, into a fluidized bed reactor.

2 kg urea / 100 kg activated carbon catalyst for depositing nitrogen up to about 0.4 wt% nitrogen content in the carbon skeleton, 3.8 kg urea / 100 kg activated carbon catalyst for 0.8 wt% nitrogen content, 6 for 1.5 wt% nitrogen content kg urea / 100 kg activated carbon catalyst was required. In order to increase the pore volume in the sample, it was necessary to put it in the fluidized bed reactor for longer.

NO conversion measurement

NO conversion was measured with test equipment for evaluation of the control sample and the catalyst prepared according to the present invention. NO conversion was measured at 120 ° C. using model flue gas (400 ppm NO, 400 ppm NH ₃ , 22 vol% O ₂ and 17 vol% H ₂ O, part: N ₂ ).

1.06 l of dry activated carbon was placed in a heated reactor and processed with model flugas at a reaction temperature of 120 ° C. The contact time was 10 seconds. During the measurement, the NO break through concentration was measured and after 20 hours the NO conversion (based on the initial NO concentration) at NO concentration in pure gas was calculated.

Example 1 (Control Example)

Samples 1 and 2 were prepared without adding nitrogenous substance urea. NO conversion was very low at 42% (sample 1) and 44% (sample 2). The small and large pore volumes of Sample 2 were much higher than Sample 1, but an increase in the extent of only a fine-measurement error in NO conversion was measured.

Example 2

The urea solution was fed to a fluidized bed reactor to yield 1-0.4 wt% nitrogen and 1-0.8 wt% nitrogen of sample. 65% NO conversion was measured for samples with 0.4 wt% nitrogen content and 71% NO conversion was measured for samples with 0.8 wt% nitrogen content.

Example 3

Various amounts of urea were fed into the fluidized bed reactor to increase the nitrogen content of the sample to 0.4%, 0.8% and 1.5% by weight, thereby yielding the sample 2-0.4% N, the sample 2-0.8% N and the sample 3- 1.5% N was obtained. As the nitrogen content in the carbon backbone increased, the NO conversion improved to 67%, 80% and 91% (1.5 wt.% N).

Example 4

Example 4 shows that, when having the same nitrogen content, further increase in the volume of small pores and large pores does not lead to an improvement in NO conversion. Rather, as can be seen in samples 4-0.4% N, 4-0.8% N, 5-0.4% N and 5-0.8% N, the volume of small pores less than 1 nm is greater than 0.34 cm 3 / g and more than 1 nm The conversion of NO was reduced from 0.45 cm 3 / g of the large pore volume of.

Examples 1 to 4 clearly show that not only the nitrogen content of the activated carbon catalyst but also the pore volume also affects NO conversion. Since the production cost of the activated carbon catalyst increases with increasing nitrogen content, and especially with increasing volume of small pores and large pores, the following improvement was performed for economic reasons.

For low NO content uncomplicated gas purification problems, catalyst types 1-0.4% N and 1-0.8% N (activated carbon catalyst according to the invention) are suitable. From an economic and technical point of view, for high NO content (> 300 ppm) in the crude gas, catalysts 2-0.4% N, 2-0.8% N, 2-1.5% N and type 3-0.4% N, 2-0.8% N This was considered a proper product.

Effect of Heavy Metals on Catalytic Activity

Since it is difficult to produce NO and heavy metal containing model gases in the laboratory, the following method has been chosen: 2-0.8% N of catalyst samples are used in pilot plants to remove NO from the actual exhaust, in addition to NOx, heavy metal arsenic and boron Also included. After 12 seconds of residence time, the 360 ppm NO content was reduced to 50 ppm. To obtain samples contaminated with arsenic and boron for use in the activity test of the NO test apparatus, after 3 days (sample 6.1.2-0.8% N) and 9 days after the initial gas level of the reactor (sample 6.2. Harvested in 2-0.8% N). Both samples collected significant amounts of arsenic and boron, but the catalytic activity was only slightly reduced from 80% (initial material) to 73% or 71%, respectively. Only at very high heavy metal content (sample 6.3.2-0.8% N) of 865 mg / kg arsenic and 7185 mg / kg boron reduced the catalytic activity to 15%. Heavy metals in the initial gas layer of the pilot plant settled, so that only 50 ppm NO was contained in pure gas after 45 days.

TABLE 1

Sample Number Pore volume (cm 3 / g) Nitrogen content (% N) Heavy metals in the catalyst % NO conversion Small pores less than 1 nm Large pores greater than 1 nm Arsenic m / kg Boron m / kg One 0.15 0.36 0.3 - - 42 1-0.4% N ˝ ˝ 0.4 - - 65 1-0.8% N ˝ ˝ 0.8 - - 71 2-0.4% N 0.26 0.41 0.4 - - 67 2-0.8% N ˝ ˝ 0.8 - - 80 2-1.5% N ˝ ˝ 1.5 - - 91 3-0.4% N 0.34 0.45 0.4 - - 63 3-0.8% N ˝ ˝ ˝ - - 78 4-0.4% N 0.4 0.60 0.4 - - 59 4-0.8% N ˝ ˝ 0.8 - - 71 5-0.4% N 0.47 0.72 0.4 - - 49 5-0.8% N ˝ ˝ ˝ - - 64 6.1.2-0.8% N * 0.2 0.41 0.8 31 2560 72 6.2.2-0.8% N * 115 1340 71 6.3.2-0.8% N * 865 7185 15

* Load 2-0.8% N of catalyst in actual emissions (contaminated with NOx, arsenic and boron) in pilot facility, remove it at gas access side after various catalyst durations, investigate NOx conversion rate in NO test facility, Evaluated.

Claims (10)

Activated characterized in that the nitrogen content in the carbon framework is at least 0.4% by weight, the pore volume of small pores less than 1 nm is 0.47 cm 3 / g or less, and the pore volume of large pores greater than 1 nm is 0.72 cm 3 / g or less. Carbon catalyst. The carbon framework has a nitrogen content of 0.5 wt% or less, a pore volume of less than 1 nm of pore volume of 0.2 cm 3 / g or less, and a pore volume of of more than 1 nm of large pores of 0.4 cm 3 / g or less Activated carbon catalyst, characterized in that. The carbon framework has a nitrogen content of at least 0.4% by weight, preferably from 0.8 to 1.5% by weight, and the pore volume of small pores less than 1 nm is from 0.2 to 0.4 cm 3 / g and greater than 1 nm. Activated carbon catalyst, characterized in that the pore volume of the pores is 0.4 to 0.6 cm 3 / g. A method for producing an activated carbon catalyst according to any one of claims 1 to 3, wherein the carbonaceous material is contacted with a nitrogenous compound. The process of claim 4 wherein the carbonaceous material is partially gasified by steam, nitrogen and carbon mixtures at a temperature of at least 750 ° C. in a fluidized bed reactor, pit furnace, rotary furnace or multilevel furnace, and the nitrogenous material is fed into the reactor simultaneously. Characterized in that the method. Activated carbon catalyst obtained according to claim 4. Use of the activated carbon catalyst according to any one of claims 1 to 3 and 6 for the removal of NOx. 8. Use according to claim 7, characterized in that the removal of NOx is carried out in the presence of a catalyst poison. Use according to claim 7 or 8, characterized in that the removal of NOx is carried out at a concentration of NOx of 300 ppm or less. Use according to claim 7 or 8, characterized in that the removal of NOx is carried out at a concentration of NOx higher than 300 ppm.